Good one. It's a comping strategy. Many jazz pianists use them with the left hand. Jazz guitarists and Gypsy Jazz rhythm guitarists use them. Probably overkill in the ukulele world. Here is one explanation.

I think TECHNICALLY a shell chord is a triad for playing an extended chord like a 6th, normally 1-3-5-6 or a minor 7th, normally 1-b3-5-7, but dropping the fifth since it has no value in determining whether it's a major/minor or what kind of extension. So a 6th shell would be 1-3-6. A minor 7th shell would be 1-3b-7.

But I think of shell chords as substitutions for implying chords when you don't have enough strings or where the voicings would be awkward. So, for a ukulele, we have to do that for any extension higher than a 7th or a 6th because we don't have enough strings.

For instance a 9th is usually 1-3-5-b7-9, but that takes five strings. Most of us don't have five strings, so the first thing to drop is the fifth: 1-3-b7-9. That would still give the flavor of the 9th. A 6/9 chord should be 1-3-5-6-9. Again, we don't have enough strings, so 1-3-6-9 would be sufficient to give the flavor of the 6/9.

If the resulting four string chord would be too difficult to grab in context, you might have to eliminate another note and duplicate one. The next one to go would probably be the root since the third determine whether it's major or minor. The 7th or 6th determines whether it's a 7th (major,dominant) or 6th extension. And of course the extension - 9th, 10th, 11th.., needs to stay.

So, that's how I think of "shell" chords. I think of them as "incomplete" chords that imply a "bigger" chord that normally has more notes in it, but for technical or artistic reasons we have to leave out some of the notes.

I think some people might think of "power" or "five" (A5 etc.) as shell chords even though they are technically an interval and not a chord because you tend to play them as 1-5-1, 1-5-1-5, etc.

You have to make extensive use of shell chords to imply extended chords on three stringed instruments like the dulcimer. You end up playing "five" chords to imply either a major or minor often when playing in secondary keys. Five chords can work as either a major or minor since they are missing the third. Nice use for a "shell".

Jim Hanks. Yes, shell voicings are used as a foundation for building chords with extended chord tones. My experience with them was on guitar and trying to learn the black art of comping.

gvalasco. Yes, but I'm just seeing the ways jazz players view the extended chord tones. Using 1-3-b7 (and 1-b3-b7) has many uses. In fact, some jazz guitarists just use the 3/b3 and b7 note chords in some situations. In a rhythm guitar comping situation, the bass player has the low root notes, and the soloist has the extended notes. You can even leave out the root note in chords, unless it is some kind of duo - 2 guitars, 2 ukuleles, etc. The rhythm guitarists in a Gypsy Jazz group will play triads, either 1-3-5, or 1-3-b7. It is the 3 and the 7 chord tones the defines the chord color.

I'll do a quick chart of what I mapped out and post it later today.

You mentioned we just have 4 strings and I'm finding that a huge plus. I have learned more songs on my tenor ukulele in the past 3 months than I ever learned on guitar - as far as strumming along with a group of musicians. I never felt capable of joining an acoustic jam. My main training is as a classical guitarist but there was no way i would be a soloist and that's what classical guitar study focuses on, solo virtuosic playing. I was a member of the Philadelphia Classical Guitar Orchestra for about 4 years but it was a very serious bunch of people. Since I left they split the guitar orchestra into a pro group and a beginner/Salon group. I may rejoin Salon group in September.

I started to practice 1-3-5 triads on the ukulele. Having just 2 string sets seems so rational. Plus, every guitar book starts with the Bass E and A strings. It makes so much sense to learn the DGBE string sets first in isolation. I see now that everything I learn on the ukulele is transferable directly back to guitar. The bass E and A strings I see now as bass notes, maybe even like a pianist's left hand.

The PDF of the 1-3-b7 triads isn't that exotic but I'll upload it anyway.

I look forward to looking at your chart Edspyhill05 , i've read a few articles on Freddie Green apparently he could make a chord out of one note , and like you say the Gypsy Jazz players use them extensively they must learn them before they learn to walk . i once went to Samois in France and watched the young gypsy players by the river bank phenomenal speed and rhythm, as they say "every days a school day".

I looked at this post and realized I did not post a pic or pdf of the 7th shell voicing that leave out the 5th of the chord. Better late than never - maybe. Triads on the reentrant ukulele make so much sense. It is a perfect triadic instrument. Compared to all the triads possible on a 6-string guitar, our humble ukulele is a dream. On a low G ukulele or baritone ukulele the possible triads offer low G or low D string notes.